It’s not too hard… you need to start the second session with (I think) these parameters:
--configdir "C:\dtvintage" --cachedir "C:\dtvintage" --tmpdir "C:\dtvintage"
configdir is the main one, I think the others are good too…
Replace the C:\dtvintage (I was trying out an early version of dt) with whatever folder you want to use (create it beforehand) to hold the database and other bits of your ‘second dt’.
In Windows a convenient way of doing this is to make a suitably named desktop shortcut and add the string into the target box:
PS ignore the fact that the screenshot shows that I called 4.2 vintage… it was actually 2.4 